The U.S. Supreme Court on Monday refused to hear a challenge to Seattle, Washington's minimum wage law brought by the northwestern city's franchise business owners.

The owners of such businesses as McDonald's argue the law requiring employers to pay workers $15 an hour is discriminatory because it gives them the same deadline to phase in the higher wages as large companies have.

The franchise owners regard themselves as small businesses, which have been given more time to adjust to the new law.

Workers' rights advocates say franchise owners get numerous benefits from their parent corporations that independent small businesses do not have.

Republican-led congressional inaction on a federal minimum wage hike has prompted several states and large cities, including Seattle, San Francisco, and New York state, to pass their own minimum wage laws.

Many business owners say they cannot afford it. But workers say they cannot live on the current federal minimum wage of $7.25 an hour, which has been in place since 2009.